mriganka mouli mondal (for star collaboration) texas a&m university
DESCRIPTION
Transverse Single-Spin Asymmetries for Jet-like events at Forward Rapidities in p+p Collisions at √s = 500 GeV with the STAR Experiment. Outline :. Mriganka Mouli Mondal (for STAR Collaboration) Texas A&M University. Forward Meson Spectrometer in the STAR experiment - PowerPoint PPT PresentationTRANSCRIPT
Transverse Single-Spin Asymmetries for Jet-like events at Forward Rapidities in p+p Collisions at √s = 500 GeV
with the STAR ExperimentMriganka Mouli Mondal (for STAR Collaboration)
Texas A&M University
APS April 5-8, 2014. Savannah, GA 1
Forward Meson Spectrometer in the STAR experiment Transverse Single Spin Asymmetries (TSSA) EM-Jets measured from FMS photons AN measurements from run-11 at √s = 500 GeV
Outline :
RHIC : the world’s first polarized proton collider
APS April 5-8, 2014. Savannah, GA 2
AGSLINACBOOSTER
Polarized Source
200 MeV Polarimeter
Hydrogen Jet Polarimeter
PHENIXSTAR
Siberian Snakes
Siberian Snakes
Spin Flipper
Carbon Polarimeters
RF Dipole AGS Internal Polarimeter
AGS pC Polarimeter
Strong Snake
Tune Jump QuadsHelical Partial Snake
Spin Rotators
Beams: √s 200 - 500 GeV pp; 50-60% polarization for year 2011
Forward ECALs in STAR
APS April 5-8, 2014. Savannah, GA 3
Forward Meson Spectrometer (FMS) :-- Pb glass EM calorimeter covering 2.5< η <4.0-- Detect 𝜋0,η, direct photons and jet-like events in the kinematic region where asymmetries are known to be large.
FMS
TSSA - 2 theoretical frameworks
APS April 5-8, 2014. Savannah, GA 4
Spin-dependent transverse momentumdependent (TMD) function ST.(PxkT) Brodsky, Hwang, Schmidt, 02Collins, 02, Ji, Belitsky, Yuan, 02
Twist-3 quark-gluon correlations Efremov & Teryaev: 1982 & 1984Qiu & Sterman: 1991 & 1999
Sivers fct.
QLQCD QT/PT <<<<QT/PT
Transversemomentumdependent
Q>>QT>=LQCDQ>>pT
Collinear/twist-3
Q,QT>>LQCDpT~Q
Efremov, Teryaev;Qiu, Sterman
Need 2 scalesQ2 and pt
Remember pp:most observables one scale
Exception:DY, W/Z-production
Need only 1 scaleQ2 or pt
But should be of reasonable
sizeshould be applicable to most pp observables
AN(p0/g/jet)
Intermediate QTQ>>QT/pT>>LQCD
π0 AN Measurements at Forward Rapidity
APS April 5-8, 2014. Savannah, GA 5
Rising AN with XF
AN nearly independent of √s No evidence of fall in AN with
increasing PT
CIPANP 2012,Steve Heppelmann
Transverse Single Spin Asymmetry
Inclusive π0 production
xF = 2pZ/√s
Run-2011 data
APS April 5-8, 2014. Savannah, GA 6
p+p √s = 500 GeV transverse datasets Jet algorithm : anti-kt R-parameter : 0.7 pT
EM-Jet > 2.0 GeV/c
FMS photons with pT > 0.001 GeV fed into anti-kt
Leading EM-Jets : Multi-photon Jets with highest energy
EM-Jets used to find asymmetry within 2.8<ηEM-Jet<4.0 40 GeV < EnergyEM-Jet < 100 GeV
# Je
ts
Structure in EM-Jet pT :-- Acceptance non uniformity in small and large tower boundary-- Different trigger threshold influence different pT region
EM-Jet characteristics
APS April 5-8, 2014. Savannah, GA 7
2-photon jets are mostly π0
Events with more than 2 photons show jet-like energy flow
No. of photons in leading EM-Jets
ϒϒ invariant mass 2-photon EM-jets
dE/d(ΔR) distribution of EM-Jets
EM-Jet Energy 60-80 GeVZ ϒϒ<0.8, no. photons =2
EM-Jet Energy 60-80 GeV
# Je
ts#
Jets
dE/d
(ΔR
) (a
rbitr
ary
scal
e)
APS April 5-8, 2014. Savannah, GA 8
EM-Jet Energy = 55-57.5 GeV
For 2-photon isolated π0
AN from fits
Individual point and χ2/NDF from averages over ~18 fills
AN is calculated from p0 + p1 cos(ϕ) fits over each fill p0 = relative luminosity, p1 = asymmetry AN’s are corrected for polarization values from fill to fill Weighted AN and χ2/NDF are calculated over entire fills
AN vs. EM-Jet Energy
APS April 5-8, 2014. Savannah, GA 9
π0-Jets –2γ-EM-Jets with mγγ <0.3 Zγγ <0.8
EM-Jets – with no. photons >2
Isolated π0’s have large asymmetries consistent with previous observation (CIPANP-2012 Steven Heppelmann)
https://indico.triumf.ca/contributionDisplay.pycontribId=349&sessionId=44&confId=1383 Asymmetries for jettier events are much smaller
AN vs. EM-Jet Energy
APS April 5-8, 2014. Savannah, GA 10
π0-Jets –2γ-EM-Jets with mγγ <0.3 Zγγ <0.8
2ϒ-EM-Jets (η + continuum) – with mγγ > 0.3
EM-Jets – with no. photons >2
Isolated π0’s have large asymmetries consistent with previous observation (CIPANP-2012 Steven Heppelmann)
https://indico.triumf.ca/contributionDisplay.pycontribId=349&sessionId=44&confId=1383 Asymmetries for jettier events are much smaller
AN for different # photons in EM-Jets
APS April 5-8, 2014. Savannah, GA 11
1-photon events, which include a large π0 contribution in this analysis, are similar to 2-photon events
Three-photon jet-like events have a clear non-zero asymmetry, but substantially smaller than that for isolated π0’s
AN decreases as the event complexity increases (i.e., the "jettiness”)
AN for #photons >5 is similar to that #photons = 5
Summary
EM-Jets are reconstructed from photons detected in the FMS at STAR.
Jets with isolated π0 have large asymmetry as seen before.Three-photon jet-like events have a clear non-zero
asymmetry, but substantially smaller than that for isolated π0’s.
AN decreases as the event complexity increases(i.e., the "jettiness”).
APS April 5-8, 2014. Savannah, GA 12
Backup slides
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PRD 86-051101
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Systematics arising from intermixing of event classes
PYTHIA simulations
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Lavg: +15%Pavg: +8%
2013 P~55%
>=